JP3368560B2 - Method for producing transition metal carbides from partially reduced transition metal compounds - Google Patents

Abstract

A transition metal carbide (e.g., WC) is prepared by the following steps. A carbon-precursor mixture is formed by mixing a precursor comprised of (i) a transition metal oxide (e.g., WOx) and (ii) a material selected from the group consisting of: a transition metal (e.g., W); a transition metal carbide (e.g., WC) and a substoichiometric carbide (W2C), in the presence of a source of carbon (e.g., carbon black) in an amount sufficient to form a reduced mixture comprised of the transition metal carbide and substoichiometric transition metal carbide, wherein the amount of the transition metal oxide and transition metal is essentially zero in said reduced mixture. The carbon-precursor mixture is heated in a reducing atmosphere (e.g., 5 percent hydrogen in argon) to a reducing temperature and for a time sufficient to produce the reduced mixture. The reduced mixture is milled in the presence of a source of carbon in an amount sufficient to carburize the substoichiometric transition metal carbide to form the transition metal upon heating in a reducing atmosphere. Finally, the milled reduced mixture is heated in a reducing atmosphere to a carburizing temperature that is greater than the reducing temperature for a time sufficient to carburize the substoichiometric transition metal carbide to form the transition metal carbide of this invention (e.g., WC).

Description

TECHNICAL FIELD The present invention relates to transition metals Ti, Zr, Hf, V, Nb, Ta, Cr and Mo.
And W carbides and solution carbides of the transition metals.

BACKGROUND ART Tungsten carbide generally has two forms: monotungsten carbide (WC) and ditungsten carbide (W ₂ C).
There is. It is well known that WC is useful in the manufacture of commercially valuable items such as cutting tools, dies and punches, while W ₂ C is generally not. fact
W ₂ C reduces the properties of the WC target, such as strength, even if it is present in only small amounts.

In making the WC items, it is common to combine tungsten carbide powder with a metal, such as cobalt, followed by heating to strengthen the WC / Co cemented carbide. This heating is performed under a pressure from vacuum to a pressure higher than atmospheric pressure.

In joined carbide parts, tungsten carbide,
Particle size, particle size distribution and particle chemistry have a great influence on the properties of the final part. As already mentioned above, W ₂ C should be avoided when producing tungsten carbide parts joined. Generally, in bonded parts, a smaller particle size results in improved strength. The smaller particle size is
Often results in higher hardness at a given cobalt loading. The non-uniformity in grain size in the joined tungsten carbide parts adversely affects the strength and surface condition of the parts after polishing. The particle size non-uniformity in the joined WC parts is primarily due to the growth of particles that grow abnormally during strengthening of the parts. The growth of these particles is controlled by the addition of particle growth inhibitors such as VC, Cr ₂ C ₃ , or TaC, or WC with the narrowest possible (ie uniform) particle size distribution.
It can be adjusted by starting with powder.

WC powders with an average particle size of less than 0.2-0.3 microns can induce the growth of unusually large particles due to the increased reactivity associated with fine particle size. Standard grain growth inhibitors, such as those mentioned above, can be used to bond bonded WC parts to the fine WC.
It has also been reported to be ineffective when sintered with powder. An important factor for sintering the fine WC powder was reported to be the particle size distribution of the WC powder (Suzuki et al., J. Jap Suk Powder & Powder Met.
Soc. Powder and Powder Met.), 19, 106-112, 197
2). That is, in order to reduce the possibility of particle growth during densification of the joined WC parts, a very fine
It is desirable to be able to increase the particle size and control the particle size distribution of WC powders (0.2-0.3 microns and below).

Typically, tungsten carbide is produced by carburizing tungsten metal. The basic process steps are usually (a) ammonium paratungstate or a stable form of tungstic acid, such as WO ₃ , W.
Roasting to O _2.83 , WO _2.65 and WO ₂ , (b) reduction of tungsten oxide to tungsten metal powder in hydrogen, (c) mixing of tungsten metal powder with powdered carbon, (d) tungsten and Carburization of carbon at a temperature of 1100 ° C or higher in a reducing (hydrogen-containing) atmosphere.

The particle size of the resulting WC is controlled by the size of the W metal powder produced in step (b) above. US Patent 33850614
As described in No. 3, the particle size of tungsten metal is mainly (1) depth of powder bed during reduction, (2) hydrogen flow rate, (3) dew point of hydrogen gas, and (4) reduction temperature. Adjusted with ,.

Smaller particle size tungsten powders are produced by increasing gas flow, reducing bed depth, lowering the dew point of hydrogen gas, and lowering the reduction temperature. By reducing the bed depth and lowering the temperature, the amount of tungsten powder that can carburize the WC in a given time period is reduced. The mechanism of particle growth has been attributed to volatile WOH species that are directly related to the concentration of water in the gas environment (US Pat.
No. 850614). The processes that require carburization of tungsten metal to produce monotungsten carbide are typically limited when producing WC powders with particle sizes of 0.8 microns or greater. The reason is that it is difficult to make W metal much smaller than this size, for example due to the pyrophoric properties of such fine tungsten metal powders. Due to the high hardness of WC, it is also difficult to grind WC to this small particle size. Even if WC can be easily ground to a fine particle size, this grinding method results in a broader particle size distribution than the originally controlled synthesis method.

Other methods of producing monotungsten carbide include the following methods. Steiger (US Pat. No. 3848062)
No.) is a volatile tungsten species such as WCl ₅ , WCl ₄ , WC.
The _{l 2, WO 2 Cl 2,} WOCl 4, WOF 4 and W (CO) _6, describes reacting with vaporous carbon source, such as volatile hydrocarbons or halogenated hydrocarbons. The vaporous carbon source is present during the vapor phase reaction in an amount at least equal to the WC stoichiometry. Then the products from this reaction,
That is, a mixture of WC, W ₂ C and carbon is roasted in hydrogen for 1-2 hours at 1000 ° C. to give monotungsten carbide substantially free of ditungsten carbide.

Miyake (US Pat. No. 4,080,090) discloses a first step in which tungsten oxide is reacted with a carbon source in a non-reducing atmosphere at a temperature of 1000.degree. , A second step of reacting at a temperature higher than the first step to produce monotungsten carbide. Miyake has specified that the temperature must be above 1000 ° C in the first step of removing oxygen.
This removal of oxygen causes hydrogen to react with oxygen to produce water vapor, which in turn reacts with carbon to produce volatile carbon-oxygen species, which results in increased particle size and depletion of second stage product. It induces a uniform carbon content and is necessary to avoid the formation of the steam.

Kimmel (U.S. Pat. No. 4,664,899) mixes tungsten oxide or ammonium tungstate with carbon powder to form a mixture, which is then heated in a non-reducing atmosphere such as Miyake at a suitable temperature. For a period of time to form a reduced mixture comprising tungsten, ditungsten carbide and monotungsten carbide, provided that the reduction reduces the carbon content of the resulting reduced mixture to 6.13 wt% or less. To produce mono-tungsten carbide comprising performing in the presence of sufficient carbon. Kimmel then determined the carbon content of the resulting reduced mixture and said that sufficient carbon was obtained to increase the carbon content to at least the stoichiometric amount required to produce monotungsten carbide. To the reduced mixture obtained and carburizing the conditioned reduced mixture in a hydrogen atmosphere to produce monotungsten carbide. Kimmel further describes that the reducing product of tungsten oxide is a mixture of W, W ₂ C, WC and free carbon, and that all of the oxides are reduced.

In order to produce monotungsten carbide, these methods are slow processes of complete reduction of tungsten compounds, such as tungsten oxide, to tungsten metal in a hydrogen-containing atmosphere, or non-reducing (ie non-reducing) tungsten compounds. It requires a slow process of reduction to a mixture of tungsten metal, tungsten carbide and free carbon in a (hydrogen) atmosphere. The tungsten or mixture produces mono-tungsten carbide without oxygen (ie, without tungsten oxide) prior to final carburization in a reducing atmosphere. Oxygen is essentially completely removed to avoid particle growth due to the formation of species such as WOH, as well as evaporation loss of carbon due to oxidation or hydrolysis during the carburization of tungsten or mixtures in a hydrogen containing atmosphere. The disappearance of carbon during carburization makes the carbon content of the resulting carbide product inhomogeneous (ie W ₂ C is present in the product). The production of fine WC powders with a uniform carbon content is problematic in industrial processes, especially because it processes large amounts of material which exacerbates the problems mentioned above.

Therefore, it would be desirable to provide a rapid industrial process for producing uniform carbon content and small grain size monotungsten carbide (WC) that avoids the problems described above.

SUMMARY OF THE INVENTION The objects of the present invention are: a) (i) transition metal oxides and (ii) transition metal carbides,
A precursor consisting of one or more materials selected from the group consisting of transition metals and quasi-stoichiometric transition metal carbides produces a reduced mixture in step (b), ie a reduced mixture Consisting of transition metal carbides and quasi-stoichiometric transition metal carbides, mixed in the presence of a sufficient amount of carbon source such that the amount of transition metal oxides and transition metals is essentially zero. Thereby producing a carbon-precursor mixture, b) heating the carbon-precursor mixture to a reducing temperature under a reducing atmosphere for a time sufficient to produce a reduced mixture, and c) the reduced mixture. Is milled in step (d) in the presence of a sufficient carbon source to carburize the substoichiometric transition metal carbide to form the transition metal carbide,
Sufficient to produce a milled reduced mixture, and d) carburize the sub-stoichiometric transition metal carbide in a reducing atmosphere to produce a transition metal carbide. Heating to a carburizing temperature higher than the reduction temperature for a period of time.

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention allows high speed production of monotungsten carbide powders of uniform particle size and chemistry, especially when the precursors contain significant amounts of transition metal oxides. The method also avoids the spontaneous ignition of tungsten metal when producing fine WC powder. The transition metal carbide powders and especially WC produced by the method of the invention are used as items such as abrasives and as ingredients in making joined carbide wear resistant parts such as cutting tools, spray nozzles and die. It is useful.

TRANSITION METAL CARBIDE The method of the present invention relates to the production of transition metal carbide. Transition metal carbides include the following transition metal carbides: monotungsten carbide (WC), monotitanium carbide (Ti).
C), monotantalum carbide (TaC), monovanadium carbide (VC), monohafnium carbide (HfC), monozirconium carbide (ZrC), mononiobium carbide (NbC), dimolybdenum carbide (MO ₂ C) or tricarbide dicarbide. Ti, Zr, Hf, V, Nb, Ta, which has a stoichiometry equivalent to chromium (Cr ₃ C ₂ ).
It is a carbide of a transition metal selected from the group consisting of Cr, Mo and W. Transition metal carbides are the ones of the carbides specified above.
One or more, or if the solid solution carbide of said carbide, eg, the stoichiometry of carbon, corresponds to the stoichiometry of said transition metal carbide (eg (W _0.5 , Ti _0.5 ) C). It may be a solid solution carbide containing W and Ti. Preferably the transition metal carbide is WC, TiC, TaC, VC,
It is a carbide selected from the group consisting of HfC, ZrC, NbC, MO ₂ C, Cr ₃ C ₂ and mixtures thereof. When the transition metal carbide is a solid solution, the solid solution carbide is preferably W, T
It is a solid solution carbide of at least two transition metals selected from the group consisting of i, Ta, V and Cr. Most preferably, the transition metal carbide is WC.

The transition metal carbide comprises at most 5% by weight of stoichiometric transition metal carbide essentially free of transition metal and essentially free of transition metal oxide. The amount of transition metal, transition metal oxide and transition metal carbide is determined by X-ray diffraction. A substoichiometric transition metal carbide is a transition metal carbide having a low transition metal oxidation state as compared to the transition metal carbides of the present invention described above (e.g., W ₂ C is a substoichiometric transition metal carbide. is there). Essentially free of transition metal and essentially free of transition metal oxides correspond to the following amounts detectable by powder X-ray diffraction. The amount of substoichiometric transition metal carbide present in the transition metal carbide is preferably less than or equal to 1% by weight, and more preferably the transition metal carbide is essentially free of stoichiometric transition metal carbide. (That is, it cannot be detected by X-ray diffraction). Suitable X
Line diffraction techniques are described in the "Test Methods" section of this specification.

Transition metal carbide is an article made from the metal carbide,
For example, free carbon can be included in an amount that does not adversely affect the joined tungsten carbide body. The amount of free carbon is preferably 0.2% by weight or less of the transition metal carbide, more preferably 0.1% or less, most preferably 0.05%.
It is the following. This free carbon is the "test method" herein.
It can be determined by the acid digestion method described in.

The number average particle size of the transition metal carbide typically has a particle size of at most 1.5 microns in diameter. The particle size is preferably at most 1 micron, more preferably at most 0.8 micron, most preferably at most 0.6 micron to at least 0.05 micron, more preferably at least 0.1 micron, most preferably at most 0.2 micron. The number average particle size can be determined by known metallurgical techniques.

Process for Producing Transition Metal Carbide The first step in the process is one selected from the group consisting of (i) transition metal oxides and (ii) transition metal carbides, transition metals and substoichiometric transition metal carbides or A precursor of more materials, forming a reduced mixture, i.e., the reduced mixture consisting of transition metal carbide and a substoichiometric amount of transition metal carbide, of transition metal oxides and transition metal Forming a carbon-precursor (CP) mixture by mixing in the presence of a sufficient amount of carbon source such that the amount is essentially zero in the reduced mixture. .

In preparing the C--P mixture, the mixing method is any suitable method, such as those known in the art. Mixing can be done with a sigma mixer, Mura-mixer, V-type mixer and cone-type mixer. If further particle size reduction of the precursor or carbon source is desired, mixing may be accomplished with a ball mill, jet mill, vibrating mill, or agitation mill such as an attritor (at
It can be performed by milling using a device such as a tritor). If the milling requires a mill media (eg, ball mill), the mill media is preferably a bonded tungsten carbide-cobalt mill media. Ball mills are the preferred mixing method. Mixing is for a time sufficient to uniformly mix the carbon source with the precursor. Generally, the mixing time is at least 15 minutes and at most 24 hours.

Carbon Source: A carbon source is carbon or a carbon compound that decomposes to form carbon under the reaction conditions of the present invention. The carbon source may be crystalline carbon, amorphous carbon, organic materials or combinations thereof. Suitable crystalline or amorphous carbons include, for example, graphite or carbon black, such as acetylene carbon black. An example of carbon black useful in the present invention is SHAWANIGAN ^™ available from Chevron Inc. Examples of organic materials include organic polymers such as phenol-formaldehyde resins, epoxides, cross-linked polystyrene, and cellulosic polymers, carbohydrates such as sugar and starch, and hydrocarbons. The carbon source may be added or may be present in the precursor. Preferably, at least a portion of the carbon source is added to the precursor that produces the CP mixture. The carbon added is preferably crystalline or amorphous carbon. Most preferably, the carbon source is carbon black.

The amount of carbon from the carbon source present in the C-P mixture reduces the concentration of transition metal oxide and transition metal to essentially zero in the reducing atmosphere (ie, carburizing them Metal carbide or quasi-stoichiometric transition metal carbide). The amount of carbon added to the precursor is typically determined by the transition metal carbide (eg, WC) produced, the amount of transition metal oxide and transition metal in the precursor and reactor, and the "reduction step (b)". It is determined experimentally depending on the reaction conditions. Generally, the amount of carbon present from the carbon source is less than or equal to the amount that theoretically completely carburizes the precursor mixture into the transition metal carbide. Generally, the amount of carbon present from the carbon source in the carbon-precursor pair will be 1 of the C--P mixture.
-15% by weight, more typically the amount is in the range 2-3% by weight of the C-P mixture.

Precursor The precursor consists of (i) a transition metal oxide and (ii) a transition metal, a transition metal carbide, a substoichiometric transition metal carbide or a combination thereof. The transition metal, when present, is at least one transition metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. Transition metal carbides and quasi-stoichiometric carbides, respectively, have been previously described. Transition metal oxides include Ti, Zr, Hf, V, Nb, T
It is an oxide of a transition metal selected from the group consisting of a, Cr, Mo and W. The oxide may be a mono-transition metal oxide (eg TiO ₂ ) or an oxide compound containing at least two of said transition metals. Carbon may be present in the precursor. The carbon that may be present is a residual reactant or is formed during the formation of the precursor. This free carbon may be crystalline or amorphous. Free carbon may originate from such carbon sources, such as carbon black, graphite or organic materials mentioned above.

The amount of transition metal oxide in the precursor corresponds to an oxygen content of at least 0.5% by weight of the precursor and generally at most 5% by weight. This oxygen concentration can be determined by the LECO analysis method described in "Test Method" herein.

By way of example, when the transition metal carbide produced is monotungsten carbide, the precursors are, for example, tungsten oxide (WO _x ) and (1) tungsten, (2) tungsten, ditungsten carbide and monotungsten carbide, or (3) It may consist of tungsten, ditungsten carbide, monotungsten carbide, and carbon.

Generally, the precursor is produced by at least partial reduction of the transition metal oxide powder by carburization or reduction with hydrogen. Examples of suitable methods for producing the precursor are:
U.S. Pat.Nos. 4,809,090, 4,644,899, 3,850,614 and 3,848,060, which are each incorporated herein by reference.
The method described in the issue is included. Preferably the precursor mixture is prepared according to US Pat.
No. 5380688 describes the rapid cerbomar (cerbo
thermal) reduction method, eg entrainment
ment) or drop method (col. 4, lines 53-68 and col. 5, lines 1-12).

Reduction of Carbon-Precursor Mixture (C-P Mixture) The second step of the process of the invention is to add the carbon-precursor mixture to
Heating at a reducing temperature under a reducing atmosphere for a time sufficient to form a reduced mixture to bring the amount of transition metal oxide and transition metal to essentially zero.

C-P mixtures typically contain substoichiometric carbides,
Heat to the reduction temperature for a time sufficient to form a reduced mixture containing at least 10% by weight of the reduced mixture. More typically, the reduced mixture contains at least 15%, more typically at least 25%, most typically at least 50% by weight of the reduced mixture of substoichiometric transition metal carbide. . The balance of the reduced mixture generally consists of transition metal carbides and may contain small amounts of free carbon, for example up to 5% by weight of the reduced mixture. The reduced mixture is essentially free of free transition metal as determined by X-ray diffraction as described above.
Also, the reduced mixture is essentially free of transition metal oxides. This corresponds to an oxygen concentration of at most 0.1% by weight of the reduced mixture, as determined by the LECO method described herein.

The reduction temperature is a temperature high enough to form a reduced mixture or a temperature below the melting point of the transition metal carbide. Generally, the reduction temperature is 900-1800 ° C. Preferably the reduction temperature is 1000-1600 ° C. The time at this reduction temperature is desirably as short as possible to produce the reduced mixture. Preferably the reaction time is at least 5 minutes, more preferably at least 15 minutes, most preferably at least 30 minutes to preferably at most 10 hours, more preferably at most 5 hours and most preferably at most 2 hours.
It's time.

The reducing atmosphere is an atmosphere capable of at least partially reducing a transition metal oxide to a transition metal in the absence of carbon at a reduction temperature. Examples of gases useful in creating the reducing atmosphere include hydrogen and hydrogen-containing inert gases. Here, the inert gas is He, Ne, Ar, Kr, Xe, An and
Rn. Preferably, this gas is 2-6% hydrogen in the argon gas mixture because the mixture provides a reducing atmosphere while the amount of hydrogen in the mixture is below the explosive limit. Conventionally, Miyake and Kimmel describe the necessity of avoiding the generation of water vapor in the reduction of transition metal oxides in order to produce uniform transition metal carbides with a small particle size. It is surprising that can be used. The use of a reducing gas at this stage improves the reaction rate and thus the capacity of a given reactor, with no appreciable change in product homogeneity or quality in the liberation. During the reduction of the C-P mixture, the atmosphere is preferably made up of flowing gas. The gas is preferably passed through to remove unwanted gas species such as water vapor. Preferably, the gas flow is 5-500 standard liters / minute per kg of CP mixture, more preferably 25-250 standard liters / minute.

The CP mixture can be heated in a batch or continuous furnace.
Suitable furnaces for heating the mixture include, for example, tube furnaces, pusher furnaces, belt furnaces, rotary furnaces, elevator furnaces, fluidized bed reactors and rotary crucible furnaces. The furnace is preferably made of materials that do not contaminate the mixture during the reaction. Preferably the furnace or reactor comprises at least the heating portion of the furnace or reactor made of carbon material. The carbon material is of a purity that does not significantly contaminate the mixture. Since commercial graphite usually has significant silicon contaminants, the graphite or carbon used preferably has less than 25 ppm silicon and total metal contaminants, more preferably less than 10 ppm.

Milling of the Reduced Mixture The third step (c) of the present invention comprises carburizing the substoichiometric transition metal carbide present in the reduced mixture to produce the transition metal carbide of the present invention. Milling the reduced mixture in the presence of sufficient carbon source. It has now been discovered that pre-carburizing milling of the reduced mixture results in transition metal carbides with uniform small particle size and carbon concentration. The use of this milling is such that the use of a reducing atmosphere in step (b) rapidly reduces the oxides and carburizes any metal in the precursor mixture, resulting in a fine and uniform transition metal carbide product. Seems to give.

The production of the milled reduced mixture by milling the reduced mixture can be carried out by known or convenient methods. Examples of milling processes include ball milling, jet milling, vibration milling, planetary milling and attritor milling. Preferably, the milling process uses milling media such as ball milling, vibrating milling, and attritor milling. For milling with a milling medium, this medium is preferably a bonded tungsten carbide-cobalt milling medium. The most preferred milling method is a ball mill.

The carbon source is the same as described above. Additional carbon can be added to the reduced mixture and milled in the same manner as described above. The amount of carbon should be sufficient to produce transition metal carbides. Generally, the amount of carbon added is empirically determined from the carbon content of the reduced precursor mixture after homogenization by milling.
Carbon is then added if necessary and further milled to mix the added carbon with the milled reduced mixture. Generally, the amount of carbon (ie, free carbon) in the mixed reduced mixture will be 0.1-5% by weight of the milled reduced precursor mixture, and more typically the amount of carbon will be milled reduced. 0.25-4% by weight of the precursor mixture.

Carburizing the Milled Reduced Mixture The final step of the process is to bring the mixture in a reducing atmosphere to a carburization temperature above the reduction temperature and to present a substoichiometric transition metal present in the milled reduced mixture. Carburizing the milled reduced mixture by heating the carbides for a time sufficient to carburize to produce transition metal carbides.

The carburizing temperature is a temperature sufficiently high to form a transition metal carbide or a temperature below the melting temperature of the transition metal carbide. Generally, the carburizing temperature is at least 10
0 ° C. higher, more preferably at least 200 ° C. higher. Generally, the carburizing temperature is 1000-2000 ° C. Preferably the carburizing temperature is 1200-1700 ° C. More preferably, the carburizing temperature is 1300-1700 ° C. The time at this carburizing temperature is desirably as short as possible to produce the reduced mixture. Preferably, the reaction time is at least 5 minutes, more preferably at least 15 minutes, most preferably at least 30 minutes and preferably at most 10 hours,
More preferably at most 5 hours, most preferably at most 2 hours.

The atmosphere is the reducing atmosphere described above. During the carburization stage, the atmosphere is preferably made up of flowing gas. The gas stream is preferably 5-per kg of milled reduced mixture.
500 standard liters / minute, more preferably 25-250 standard liters / minute.

The carburizing step can be carried out in the batch or continuous furnace described above.

Test Methods The following are the transition metal carbides, C-P, described herein.
Typical methods for analyzing mixtures, reduced mixtures and milled reduced mixtures.

Carbon: Carbon concentration was determined using a "LECO" IR-212 Carbon Analyzer ^™ . For analyzer calibration, a 6.16 wt% carbon tungsten carbide standard supplied by "LECO" was used.
The analyzer was calibrated with at least 4 standards analysis samples as described by the manufacturer (LECO). Each sample and standard was analyzed with a LECOCEL II ^™ spoon and iron tip. This spoon was provided by the manufacturer (LECO). At least 4 samples are analyzed.

Oxygen: Oxygen concentration was determined using a "LECO" TC-136 Oxygen Analyzer ^™ . A standard of 0.0246 wt% oxygen was used. The oxygen analyzer was calibrated with at least 4 standard analytes as described by the analyzer manufacturer. Sample is 0.2g in tin capsule and nickel basket supplied by manufacturer
Was analyzed. At least 4 samples were analyzed.

Surface area: Surface area was determined by nitrogen gas adsorption as described by the BET (Brunauer, Emmett and Teller) method. This analysis is based on Quantachrome
Autosorb) 1 analyzer (Quantachrome, Syosset, NY)
I went there.

Free carbon: Free carbon is the amount of sample such as transition metal carbides (eg WC) acid chewed in hydrofluoric acid and nitric acid, the carbon residue is filtered with a silver filter, and the carbon on the silver filter. Was determined by analysis by the method described above for determining carbon concentration.

Phase determination: The quantification of phases and different phases was determined analytically by X-ray diffraction.
Phase quantification was determined by methods involving the ratio of peak height or peak area between peaks from different phases. For example W ₂
The amount of C is in the "d" interval of 2.276 angstroms.
Calculated from the ratio between the heights of the WC peaks at the "d" intervals of 2.518 and 1.884 Å, which is twice the height of the W ₂ C peaks.

The following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention.

Examples Example 1 Milled media of 112.7 mm diameter WC-6 wt% Co 3630 kg
A particulate mixture was prepared by ball milling 332 kg of WO ₃ and 68 kg of carbon (C) for 0.2 hours in a 2270 liter ball mill containing. This tungsten trioxide (WO
₃ ) has an average particle size of 5.2 microns and a surface area of 5.0 m ² / g, and is based on TACOW Trade Co.
nsultants Ltd., Owego. New York) under the trade name Scopino Yellow Oxide. Carbon black (C) is Chevron Shawigenen acetylene black (Chevron Shawi
nigen Acetylene Black). The surface area of these powders was determined by nitrogen using a Quantachrome Autossorb 1. After ball milling, the powder mixture was passed through a coarse sieve (8 mesh, 2.36 mm) to remove mill media.

130 kg of the granules mixture was added to U.S. Pat.
It was placed in the feed hopper of a vertical graphite tube reactor of the type described in 80688. The furnace tube was 3.25 m long and had an inner diameter of 15.2 cm. The supply hopper has a two-axis loss
It was connected to the cooled reactant carrier of the furnace by a loss-in-weight feeder. The reactant carrier had an inside diameter of 1.3 cm and was maintained at a temperature of about 10 ° C. with water flowing through the cooling jacket surrounding the reactant carrier.
After loading the particulate mixture, the feed hopper was purged with argon gas for 30 minutes, while the furnace tube was brought to a temperature of 1810 ° C as measured by an optical pyrometer looking at the outer wall of the reaction chamber. Argon gas was flowed through the reactant transporter at a rate of 170 standard liters per minute.

The particulate mixture was then fed from the feed hopper to the cooled reactant transporter at a rate of 30 kg / hr by a twin screw feeder. The flowing argon gas was entrained with the particulate mixture and fed it to the reaction chamber as a dust cloud. The particulate mixture is placed in the reaction chamber at about 10,000-100 per second.
Heated at a rate of 000000 ° C. The average residence time in the furnace of the particulate mixture was 3-4 seconds.

After exiting the heating zone of the reaction chamber, a gaseous mixture of flowing argon and carbon monoxide (produced during the Carbo-Samar-reduction reaction) transfers the product (referred to as raw material precursor) to a water cooled stainless steel jacket. The raw material precursor was carried and rapidly cooled to 10 ° C. or lower. After exiting the reactor, the raw material precursor was collected in a plastic bag inserted in a stainless steel drum.

5 kg of the raw material precursor was homogenized with 9.0 kg of WC-6% Co milling medium having a diameter of 12.7 mm for 2 hours in a 1.6 gallon ball mill to form a precursor. This precursor is used in LECO melting and combustion equipment (LECO Corp., St. Joseph.
It had an oxygen concentration of 1.05% by weight and a total carbon concentration of 6.15% by weight, as measured by MI). Then, 23 g of C (Chevron, Schauigen, acetylene, black) was added to the precursor, and the mixture was ball-milled for another 2 hours to obtain a carbon-precursor mixture (CP mixture). The CP mixture was then placed in a graphite pusher furnace using a graphite boat containing 14 g of each CP mixture.
It was treated at 1400 ° C. for 100 minutes. The final treatment is argon 9
It was carried out in an atmosphere of flowing 5% and H ₂ 5% (182 standard liters / minute · kg).

The reduced mixture was homogenized as described above. After this homogenization, the reduced mixture had a total carbon concentration of 6.02% by weight, a free carbon concentration of 0.15% by weight, an oxygen concentration of 0.17% by weight and a surface area of 1.86 m ² / g. Then, 5 kg of the reduced mixture was added to 8 g of carbon (chevron.
Milled with Schauigen acetylene black) to give a milled reduced mixture.

The milled reduced mixture was 1800 ° C. for 100 minutes using the graphite pusher furnace and boat described above.
Heated to. The monotungsten carbide product had a total carbon concentration of 6.15 wt%, a free carbon concentration of 0.02 wt%, an oxygen concentration of 0.08 wt%, and a surface area of 0.89 m ² / g.

Example 2 In Example 2, (1) the precursor had an oxygen concentration of 1.5% by weight and a carbon concentration of 6.51% by weight, and (2) 5 kg of the precursor was mixed with 14 g of carbon to form a CP mixture. Example 1 except that 5 kg of the produced and (3) reduced mixture was milled with 9 g of carbon to a milled mixed mixture.
Was the same as

The reduced mixture had a total carbon concentration of 6.00 wt%, a free carbon concentration of 0.20 wt%, an oxygen concentration of 0.15 wt%, and a surface area of 1.05 m ² / g after homogenization. Monotungsten carbide product has a total carbon concentration of 6.14% by weight, 0.03% by weight
Free carbon concentration, 0.08 wt% oxygen concentration, and 1.01 m ²
It had a surface area of / g.

Control Example 1 The precursor was the same as that used in Example 1. C2
8 g (Chevron Schauigen Acetylene Black) was added to 5 kg of precursor and the mixture was ball milled for 2 hours as described in Example 1 to give a carbon-precursor mixture (CP mixture). Then the CP mixture,
Using the graphite pusher furnace and graphite boat as described in Example 1, treatment was carried out for 120 minutes at 1600 ° C. to obtain the final monotungsten carbide. This final treatment consists of flowing Ar 95% and H ₂ 5% (162 standard liters / min.
kg).

The final monotungsten carbide product had a total carbon concentration of 6.12 wt%, a free carbon concentration of 0.09 wt%, an oxygen concentration of 0.10 wt%, and a surface area of 1.02 m ² / g.

Control Example 2 The precursor was the same as that used in Example 2. C2
1 g (Chevron Schauigen acetylene black) was added to 5 kg of precursor and the mixture was ball milled for 2 hours as described in Example 1 to give a carbon-precursor mixture (CP mixture). Then the CP mixture,
Using the graphite pusher furnace and graphite boat as described in Example 1, treatment was carried out for 120 minutes at 1600 ° C. to obtain the final monotungsten carbide. This final treatment consists of flowing Ar 95% and H ₂ 5% (182 standard liters / min.
kg).

The final monotungsten carbide product had a total carbon concentration of 6.10 wt%, a free carbon concentration of 0.16 wt%, an oxygen concentration of 0.09 wt%, and a surface area of 1.00 m ² / g.

From Examples 1 and 2 and Control Examples 1 and 2, the two-step process of the present invention (ie, heating the CP mixture and the milled reduced mixture) is less than a single heat treatment of the precursor. It is clear that it gives a free carbon concentration of the final monotungsten carbide.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Henry, Jiyoung Pee, Midland Cayade 5640, Michigan, USA 5900 (72) Inventor Delka, Pat Jei 48642 Midland Autumn Ritsuji Circle South 4416, Michigan, USA 72) Inventor Bunnel, Tom The Ray, Michigan, USA 48640 Midland Leeway 5918 (72) Inventor Repman, Joseph Joseph F, Michigan, USA 48640 Midrand Pine Wood Drive 4812 (72) Inventor Kyaroll, Daniel Ehu 48640 Midland Sylvan Lane 701, Michigan, USA (72) Inventor Anderson, Stephen A. 48657 Sanford, Michigan, USA Estosaginoh Road 2288 (56) Reference US Patent 4664899 (US, A) US Patent 5380688 (US, A) International Publication 95/21946 (WO, A1) International Publication 97/10176 (WO, A1) (58) Field (Int.Cl. ⁷ , DB name) C01B 31/30-31/36

Claims (15)

(57) [Claims] 1. Comprising one or more materials selected from the group consisting of (i) transition metal oxides and (ii) transition metal carbides, transition metals and substoichiometric transition metal carbides. The precursor forms a reduced mixture in step (b), i.e. the reduced mixture consists of a transition metal carbide and a substoichiometric transition metal carbide, the amount of transition metal oxide and transition metal being essentially To produce a carbon-precursor mixture by mixing in the presence of a sufficient amount of carbon source to bring the carbon-precursor mixture to a reduced mixture. Heating to a reducing temperature under a reducing atmosphere for a time sufficient to allow: c) carburizing the reduced mixture in step (d) with a substoichiometric transition metal carbide to form a transition metal carbide. Enough carbon for Mill in the presence of a source,
Sufficient to form a milled reduced mixture, and d) carburize the sub-stoichiometric transition metal carbide in a reducing atmosphere to produce a transition metal carbide. Heating to a carburizing temperature higher than the reduction temperature for a period of time. 2. The method of claim 1 wherein the precursor is produced by an adjoint process. 3. The method of claim 1 wherein the precursor comprises tungsten, monotungsten carbide, ditungsten carbide, free carbon and tungsten oxide of formula WO _x . 4. The transition metal carbide is WC, TiC, TaC, VC, Hf.
The method of claim 1 selected from the group consisting of C, ZrC, NbC, Mo ₂ C, Cr ₃ C ₂ and mixtures thereof. 5. The transition metal carbide is WC, claim 4
the method of. 6. The method of claim 1 wherein the milling in step (c) is ball milling. 7. The method according to claim 1, wherein the reduction temperature is 1000 to 1600 ° C. 8. The method according to claim 1, wherein the carburizing temperature is 1200-1800 ° C. 9. The method of claim 1 wherein the reducing gas is 2-6% by volume hydrogen in an inert gas. 10. The method of claim 1 wherein the inert gas is argon. 11. A process according to claim 1 wherein the transition metal carbide comprises free carbon in an amount of at most 0.1% by weight of transition metal carbide. 12. Free carbon is at most 0.05 of transition metal carbide.
The method of claim 11 which is in weight percent. 13. The method of claim 1 wherein the reducing atmosphere is a flowing gas. 14. The method of claim 1 wherein the transition metal carbide has a particle size of at most 1.0 micron in diameter. 15. The method of claim 1 wherein the transition metal carbide has a particle size of at most 0.8 microns in diameter.